Wave-transmission control circuits



WAVE .TRANSMISSION CONTROL CIRCUlTS Filed Dec. 5o. 1922 v, rality of channels in a modulator and Patented 1 Jan. 4, 1927.

PATENT.. oFFi'cE.'

JOHN MILLS," OF WYOMING, NEW JERSEY, ASSIGNOR T0 WESTERN ELECTRIC' CM- PANY, INCORPORATED, OF NEW WAVE-TRANSMISSION coNTRoL CIRCUITS.

Application" filed December 30, 1922. Serial No. 609,885.

This invention relates to wave transmission systems and more particularly to systems for controlling the transmission of signals in a carrier wave system.

It has been found that many types of signals transmitted over communicationl circuits contain or are associated with waves having peaks considerably in excess of the average value of the wave peaks transmitted. For example, voice waves usually contain excessive peaks which occur more or lessI irregularly from time to time in the course of transmission of said waves, and are not essential to an understanding of the speech. When the peaks ina voice Wave are applied to a modulator, .the load thereon rises to an excessive value ascompared to the normal load. These excessive peaks may also produce excessive loads on any ampliers which transmit the voice wave to the modulator or that receive the modulated wave therefrom.

In a multiplex carrier .wave system where several channels, having separated frequency ranges, transmit carrier waves over a common path or medium,

may be of sufficient amplitude or power to produce appreciable disturbingcurrent in an unrelated channel even though said channels are ordinarily capable of operating without mutual disturbance when waves of normal amplitude are transmitted therethrough. When a repeatery common to a plumultiplex system is employed to repeat simultaneously a plurality of signals, the presence of excessive peaks in one carrier wave may result in overloading the repeater, thereby causing the repeater to distort one or more of the simultaneous signals and to intermodulate the various waves being repeated. This causes cross-talk between the different channels and also` produces other disturbances therein.

One object of the present invention Iis to reduce cross-talk or disturbances in a carrier wave transmission system.

Heretofore it has been sary to the like considered necesprovide modulators, repeaters and of large power output in order to 'avoid the disturbing effects of excessive peaks in the signal wave. One object of the provide methods and means. for reducing the size of carrier wave associated apparatus rean excessive peakv transmitted on a carrier wave in one channel lmeans to limit the amplitude of modulating waves transmitted therethrough to a predetermined maximum value, while the unsuppiessed portion of said modulating wave is transmittedA Without appreciable distortion to a modulator in which a carrier wave 'is modulated in accordance with the unsuppressed portion of said modulating wave. The wave transmitted from said power limiter cannot exceed a fixed maximum value, and the apparatus receiving energy from said power limiter is therefore subjectled to a smaller and definitely limited load.

This apparatus may consequently have a smaller power rating, whereby under normal conditions the modulator and associated repeaters may be operated more efficiently than in the case where apparatus, such as modulators of larger power output, are operated at a power output considerably lower than the maximum. f

These and other objects of the invention will beapparent from the following more detailed description when taken in connection with the appended drawing and claims. In the drawing the figure shows a schematic diagram of connections for a multiplex carrier wave system in which the substation l, labeled S, may include any usual type of transmitting and receiving apparatus adapted for telephony, telegraphy, signaling or the like; Station 1 is connected by a transmission line or circuit 2 to the hybrid coil or balanced transformer conneet-ion 3 to which is yconnected the usual form of balancing network 4labeled N, the east-going channel, labelled E1, and the West-going channel, labelled .Wr The signal or modulating wave is transmitted to the power. limiter 5, labeled PL, which is shown as a relay or amplifier of the space current type of a form Well-known in the art. The temperature of the cathode 6 may be varied by varying the resistance 7 in series with the energizing source for the cathode 6. It is wellknown that by reducing the temperature of the cathode 6 to the proper value, a wave impressed upon the power limiter 5 will be repeated with the exception of itsy l n y resistance power limiting peak values. peak values are suppressed 1or choppedfot and are not transmitted out fromthedimiter 5. The degrees to which the impressed wave is suppressed or is not transmitted depends upon the degree to tial 8 be adjusted so that the limiter 5 operates at the center of its space current characteristic. When a wave of sufiicient amplitude is impressed on .the power limiter, a positive half of said wavewill be transmitted through the limiter with a Amaximum value equal to that of the negative half wave transmitted therethrough. 1n practice the power limiter 5 is adjusted by means of the 7 or by other well-known means to transmit without distortion substantially the entire signal wave impressed thereon, the adjustment being such that portions of the signal wave having peaks considerably in excess of the average value of the peaks in said signal Wave are suppressed by the power limiting action described above. Any other well-known type of substantially distortionlessv repeater having a controllable action,l such as described above in connection with the limiter 5, may be employed in place of `a repeater of the space current type. The unsuppressed portion of the signal wave is impressed on the modulator 9,'labeled M, which is an electric relay having a non-linear transmission characteristic and may be of the type disclosed in U. S. PatentvNo. 1,350,752 to Van der Bijl, granted August 24, 1920, or of an. other well known type. Carrier waves mo ulated in accordance with the signal or modulating wave are transmitted through the band filter or other selective circuit 10, labeled F, which transmits only.V those waves which are essential to the intelligible reception of the signal at the receiving station. Filter v10 may be of the type disclosed in U. S. Patent N0. 1,227,113 ed May 22, 1917. Waves transmitted through ltei' 10 are conveyed over the trans- `mitting path 11 common to a plurality of east-going channels El, E2, etc., and to the hybrid connections 12 provided with the usual form of balancing network 13. Carrier waves are transmitted from th hybrid connections 12 over line 14 to the two-way repeater 15, labeled R, and from thence to the terminals of a distant receiving station of the same character as the system of circuits shown in the` gurehterminating to the left of the line circuit 14.

Waves transmitted to station 1 from the distant station are conveyed over line c ircuit 14 through hybrid connections 12 over the receiving path 20 common to a plurality of west-going channels W1, W2, etc., and to the to Campbell, grantj the transmission o filter or selective circuit 21 in channel W,. Filter 2l, which may be similar in type to filter 10, selects waves intended for the channel W, other channels VZ, mon. receiving path 20. The demodulator or the detector 22, labeled DM, connected to the output of filter 21 converts the modulated carrier wave for channel W1 into a wave of signal frequency which is transmitted through the hybrid connections 3 and the line circuit 2 to the substation 1.A

The power transmitted lthrough each channel E1, E2, etc., is limited by a power limiter '5 individual to the modulating circuit included in said channel, so that inno instance may the amplitude or power of signals in any one channel be great enough and excludes waves intended for etc. connected to the com' to cause disturbances lin an unrelated chansimultaneously. It is thus seen that the repeater 15 is never subjected to a load in excess of a fixed value and may, therefore, be operated as near as desired to its rated capacity without exceeding said capacit Although voice waves have been referred to in connection with the description of the invention, it is to be understood that any electric waves having similar characteristics to voice waves may be controlled in a similar manner and for the same purpose as described above in connection with voice waves.

The invention nection with a specific circuit embodiment but the invention is not to be limited tothe specific form of circuit shown. It 1s clear that various modifications of' the means and vtransmitted over all the channels has been disclosed in conmethods disclosed are possible without de.-

vention. The scope of the invention is more specifically defined in the appendedv claims.

What is claimed is: j

1. -In a multiplex carrier wave system, a plurality of communication channels, each of said channels including a circuit for transmitting modulating waves and a circuit for transmitting carrier waves modulated by said modulating waves, a common path for all of said channels, and means in each said iirst mentioned circuits to limit to a predetermined value, the power transmitted by said channel to said common path.

2. In a multiplex carrier wave system, a plurality of communication channels, eachof sai channels including a circuit for transmitting modulating waves and a circuit for transmitting carrier waves modulated -by said modulating waves, a .common pathlfor all of said channels, a repeater -in said common path, and means in each of said first mentioned circuits to limit to a .predetermined value, the power transmitted to said repeater: carrier wave system, the

method of operation which comprises sup- 'modulating wave.

cies, b power value intended for said other channels, the method to prevent crossstalk in said common p f a predetermined value and modulating said carrier wave in accordance with substantially the entire unsuppressed Wave.v

5. An electric relay having non-linear transmission characteristics whereby the outcarrier waves, a modulator for of operatinoput of said relay is impressed .input energy, means for supplying input energy thereto, and a power 1im iting device connected to receive energy from said means and t0 impress energy directly upon said relay, said power limiting device eing capablev of transmitting only energy not in excess of the amount beyond which the outputenergy of said relay does not change.

6. In a carrier wave system, a. circuit for transmitting modulating waves,

carrier waves in accordance with a transmission circuit for transmitting the resulting modulated waves, d circuit serving simultaneously for the" transmission of other waves and means for reducing interference between the waves JOHN MILLS.

not proportional to the i 

